Video tape editing control systems are described in U.S. Pat. No. 4,040,098, and in copending application Ser. No. 23,759, filed Mar. 23, 1979, now U.S. Pat. No. 4,272,790, both of which are assigned to the present assignee. These editing control systems are capable of controlling one or more source video tape recorders so that selected portions of the video information from the source video tape recorders may be recorded on a record video tape recorder, with any particular portion of the video information terminating at a selected edit point at which a second different portion commences. In these editing control systems, the portions of the video information change abruptly at the selected edit points.
Systems are known to the prior art, however, for causing each of the portions of video information to "dissolve" into one other at the edit points, instead of abruptly changing from one portion to the next. However, for a true dissolve, it is necessary for two source video tape recorders to be controlled by the editing control system simultaneously as a selected edit point is approached and passed, the video information from the first source video tape recorder is decreased to a minimum and the video information from the second source video tape recorder is increased to normal amplitude so that the video information from the first source video tape recorder is gradually replaced by the video information from the second source video tape recorder, and there is no abrupt transition from one to the other.
However, such a true dissolve requires that the two source video tape recorders be exactly in synchronism, or else distortions will occur during the dissolve period. Such synchronization requires expensive time-base correction circuitry and mixer circuitry. An example of such a true dissolve system, together with the required time-base correction circuits and mixer circuits may be found, for example, in Ettlinger U.S. Pat. No. 3,721,757.
In accordance with the present invention, however, dissolves are simulated without the need for such expensive time-base correction circuits and mixer circuits. This is because no effort is made in the system of the invention to control both source video tape recorders at the same time. Instead, as an edit point is approached, one of the video tape recorders is controlled to reduce the video signal portion of the video information being recorded gradually to a minimum, while the amplitude of the synchronizing signals remains unchanged. This creates a gradual decrease in the video signals being recorded on the tape in the record video tape recorder without any loss in the synchronizing signals, and with no distortion. Then, when the edit point is reached the recording is stopped. Now the second source video tape recorder and the record video tape recorder are cued back and rolled forward together, and only the second source video tape recorder is turned on with its synchronizing signals being recorded with full amplitude, as its video signals are gradually increased. The transition from the synchronizing signals of the first video information to the synchronizing signals of the second video information occurs between frames, so that there is no visible distortion.
When the video information recorded on the tape in the record video tape recorder is reproduced, the screen phosphor delay characteristics of the cathode-ray viewing tube of the reproducing equipment gives the appearance of a true dissolve as each edit point is approached and passed, although only the video information from a single source video tape recorder is being recorded at any one time, and although no attempt is made to control simultaneously two source video tape recorders.